5.9-1 Am I allowed to make a picture of the recently built building LAC (Lugano Arte e Cultura) in Lugano, and produce some nice t-shirts with this picture in order to sell them at the local tourist shops?

Yes you can do that according to art. 27 CopA. The building is protected by copyright, however, as it is placed on public ground and accessible to the public, the exception of art. 27 CopA applies. Under this exception it is also allowed to use the reproduction of the work for commercial purposes.